Jim Michalak's Boat Designs

(1may02) This issue will discuss butt joints in plywood sheets. The
15may02 issue will present an essay about building the HC Skiff.

ON LINE CATALOG OF MY
PLANS...

... can now be found at Duckworks
Magazine. You order with a shopping cart set up and pay with credit
cards or by Paypal. Then Duckworks sends me an email about the order
and then I send the plans right from me to you. The prices there are $6
more than ordering directly from me by mail in order to pay Duckworks
and credit charges. The on line catalog has more plans offered, about
65, than what I can put in my paper catalog and the descriptions can be
more complete and can have color photos.

NOTE, 26APR02, THE DUCKWORKS MANAGER IS ON VACATION FOR A FEW WEEKS
RIGHT NOW AND IT IS NOT CLEAR TO ME AT ALL HOW THE PAYPAL ORDERS ARE
BEING HANDLED! SO UNTIL FURTHER NOTICE (WHEN CHUCK GETS BACK FROM
VACATION) I'D GREATLY APPRECIATE IT IF YOU DID NOT ORDER THROUGH
PAYPAL. YOU CAN USE THE ONLINE CATALOG TO MAKE A CHOICE, THEN SEND YOUR
ORDER TO ME BY SNAILMAIL AND PAY WITH A CHECK, REDUCING THE DUCKWORKS
CATALOG PLANS PRICES BY $6.

THE KEYSTONE MESSABOUT, at Keystone Lake, Oklahoma, will take place May
11-12. Click here for details.

THE 13th ANNUAL MIDWEST HOMEBUILT BOAT MESSABOUT will take place on
June 8 and 9 at the Gun Creek Recreation Area at Rend Lake in Southern
Illinois. Take exit 77W off I-57, head towards the golf course and you
will see the signs. Lots of people arrive on Friday and leave early on
Sunday. The camping fee is now $10 which includes the ramp fee at this
Corps of Engineers facility. There is no schedule of events. We have a
pitch in dinner on Saturday evening.

THE LAKE CONROE (HOUSTON, TEXAS) MESSABOUT of April 13 was a big
success. Look at a report with lots of good photos at Shortypen's boat page

Left:

Bob Williams' IMB at the Houston Messabout.

Contents:

Contact info:

JOINING PLYWOOD SHEETS

BACKGROUND...

Almost any boat you build from plywood will require panels longer than
the 8' lengths you will find at the lumberyard. For an "instant boat"
the usual manner of joining the panels together to get one long panel
is with a butt strap or butt plate. I've tried lots of different ways
to make the joint in the 15 or so boats I've built over the years. All
the methods worked. I have a feeling that the butt joints on the usual
instant boat hull are not highly loaded and not too critical to overall
boat strength. Since I've tried several ways and they all worked I've
gotten to be pretty nebulous about the subject on my drawings. Lately
I've been specifiying a butt plate as something like "Butt plate from
3/4" x 3-1/2" lumber, or equal" which doesn't tell you much. Most
builders get by pretty well with just that but recently one builder
asked what in the world I meant, and rightly so. So let's start the
discussion with one joint I've never tried in plywood.

TRADITIONAL PLYWOOD SCARF JOINT...

Figure 1 shows the traditional plywood scarf joint. I''ve never done
this in plywood although I've made a lot of scarf joints in plain
lumber. The two overlapping faces are tapered and glued together such
that both joined faces remain smooth. If you are building a traditional
lapstrake boat from plywood you have to make the joints this way.

What good about it? The faces are smooth both sides. Essentially you
have a single piece of wood to work with after making the joint. It's
quite strong, as strong as the base wood provided the taper is long
enough. I've seen the taper range from 6:1 to 12:1. The shorter tapers
are easier to make and probably just as good given modern glues.

What's bad about it? The tapers can be hard to make properly although
thickened epoxy has made experts of most of us. Some experts have
special saw rigs to cut the taper. Most use power hand planes or belt
sanders, I think. When gluing the joint you must press it up against a
firm surface while the glue cures, making sure nothing glues to that
surface, and making sure the two pieces are secured lengthwise so the
tapers don't push them apart as you apply clamping pressure.

There is one more warning for instant boat builders. Almost all instant
boat designs have panels layouts which assume you will not be using a
scarf joint. If you join two 8' panels with a scarf joint you will NOT
end up with a 16' panel. It will be shorter by the overlap amount. That
might be just enought to negate the ply panel layout.

THE PAYSON TEAL BUTT STRAP...

I think this type of joint was described in Payson's great book INSTANT
BOATS. I used it on my Teal which was my first homemade boat. The side
panels were 1/4" thick on my boat, the bottom 3/8". The butt straps
were 3/8" plywood, 6" wide. So the effect of the joint was similar to a
12;1 scarf on the 1/4" ply sides and about 8:1 scarf on the bottom. The
nails were supposed to be copper, but I think Harold might have also
suggested copper rivets or short bolts for fasteners.

What's good about it? It's pretty simple to visualize and make. If the
fastening is good you can make the joint and go right on building
without waiting for the glue to set. You might do that with the sides,
for example. Another neat thing about this plain butt strap joint is
that, with a typical flat iron skiff type of assembly, the bottom
panels need not be joined before assembly onto the hull. In that case
you will have the hull inverted on sawhorses ready for the bottom. Then
you put the first bottom piece on attaching it to the sides. Then you
install the first butt strap at the end of that piece. Then you install
the next bottom panel to that butt strap and the sides. And so forth
until the entire bottom is planked, like laying bricks.

I might mention now that I think butt straps and plates should be well
rounded at the ends to avoid trapping dirt and moisture. In boats that
have taped seams I advise stopping the butt strap short of the edge of
the panel so you will have room to run the tapes undisturbed. This is
especially true of butt straps on the bottom. You must have a clear
limber channel around the perimenter of the bottom. In that case I stop
the strap about 1/2" short of the side, fill the little gap with epoxy
to keep the water out, and tape over the bottom of the joint with glass
tape and epoxy. Usually I don't put glass tape over the outside of the
side panel joints. But butt joints in any deck should be well sealed
with glass and epoxy. Here is an end view of the treatment:

What's bad about the plywood strap? I think in Maine you aren't a man
until you've made a boat with clenched copper nails or rivets. Not so
where I live, can't buy them any place I know of. I got by with bronze
boat nails but they really aren't flexible enough for the job. They
didn't look too cool. And the edges of the plywood butt straps don't
look too cool either, wanting to have gaps and splinters showing. It
takes a while to finish them. And, of course, you have a lump at each
joint and folks will ask, "What's that?"

By the way, when I built my Toto I used the simple plywood strap method
with no fasteners. Just carefully lay the ply panels over the straps
which were well buttered with glue, weighed it all down with concrete
blocks to provide pressure, and stayed away for a few days until I was
sure the glue was totally set.

THE BIRDWATCHER BUTT STRAP...

When I built my Birdwatcer in 1988 I think I piled on more layers of
plywood straps such that I wouldn't have to bend over the nails. And by
that time I was more expert at finishing the edges of plywood. It
worked but it was very obvious that I could have done the same thing
with regular lumber and saved a bit of work.

THE LUMBER BUTT PLATE...

This is I like to advise now. Not much to it. Very quick and easy to
make. Some say it looks too clunky for their tastes.

If there has been any structural problem with the above butt plate it
is at the ends of a plate that joins bottom panels, ending short of the
sides to allow a limber path. If the ends of the plate are not solidly
glued and fastened to the bottom panels the butt plate will eventually
loosen at the ends. I think that is due to the rapid change in
flexibility in the system where the plate suddenly ends. A better
solution might be to taper the end of the bottom butt plates starting
maybe 3" in from the end of the plate and tapering down to maybe 3/8"
thick at the ends. That will allow a gradual change in the flexibility
and prevent a stress riser at the end of the butt plate. By the way,
for any bulky butt joint care must be taken in design to see that the
joints don't fall in places where the butt plate will be in the way.

LIGHT FIBERGLASS BUTT JOINTS..

Both Harold Payson and Dave Carnell presented this one to U.S. readers
in the '80's but I'll bet the English inventors of taped seam boats did
it earlier. Simple as can be in theory. Just a layer of fiberglass on
each side of the plywood.

Dave Carnell
presents lots of details at his web site. He has done scientific load
tests of these joints and says the joint will be as strong as the base
wood if you use one layer of fiberglass cloth in epoxy on each side of
1/4" plywood, two layers on 3/8" plywood, three layers on 1/2" plywood,
and four layers on 3/4" plywood.

I used the glass butt joint on my Roar rowboat but went back to wooden
butt joints later. At first it would appear that the joint is easily
made by laying the ply pieces on the floor, taping one side with
fiberglass, waiting to cure, flipping the panel and repeating on the
other side. But I found that plywood on its own often does not want to
lay flat enough to get a smooth fit, so I had to place the joint over a
board and screw the pieces down flat. Next the idea of flipping the
panel with only one side taped doesn't work well because that one layer
of glass has little strength by itself. But it can be done carefully.
Better yet is what both Payson and Carnell advise: glass both sides at
once. Lay the first side of fiberglass layers wet with epoxy on a
protected flat surface, lay the plywood to be joined upon it, lay the
second side of fiberglass over the top of the joint, cover with plastic
sheet and weigh down with concrete blocks. The plastic sheeting not
only protects everything from gooey epoxy, but it should provide a
smooth final finish and if you are lucky no filling or sanding required
afterward.

THE PAYSON HEAVY GLASS JOINT...

Harold Payson did a little more work on the glass butt joint. I'm doing
this from memory and hope I'm getting it right. To hide the build up of
glass on a thicker sheet of plywood he recessed the surfaces roughly
with a sanding disk in a drill. Then he added a layer of light
fiberglass matt to the wood before pasting in the glass. Fiberglass
matt is generally thought to provide better adhesion to wood than glass
cloth although by itself it has little strength. Harold is big on using
polyester resin on his boats instead of epoxy so perhaps the matt is
more important for the polyester users. But you can see the advantage
of the system: the final joint can be more or less invisible as the
multiple layers of glass are recessed.

IMB

IMB, SAIL BEACHBOAT, 13-1/2' X 5-1/2', 350 POUNDS EMPTY

The prototype IMB was built by Jerry Scott of Cleveland, Texas. (This
boat was originally drawn for a design competition sponsored by
International Marine Publishing a while back and was called the
International Marine Beacher, or IMB. I didn't win anything (again).) A
second IMB was completed recently by Bob Williams, also in Texas.

IMB features a "Birdwatcher" cabin. Birdwatcher cabins are full length
with panoramic watertight windows and a center walkway slot in the
roof. Everyone rides inside including the skipper.

Around 1984 Phil Bolger showed me a cartoon of his 24' Birdwatcher and
I didn't know what to think of it. He presented it in a 1986 issue of
the old Small Boat Journal. Ron Mueller built the prototype and
convinced me that this cabin really works. I built the second
Birdwatcher and here is what I found:

These boats can be self righting without ballast because the crew
weight works as ballast. They sit down low on the floor looking out
through the windows (although I found standing in normal winds was
quite acceptable). In addition, the high cabin sides provide lots of
buoyancy up high to ensure a good range of stability. IMB, which is
small and has no ballast, will probably self right from 60 or 70
degrees of heel, but the larger ones such as the water ballasted Scram
will self right from a full 90 degrees knockdown. Others like the
original Birdwatcher and my Jewelbox have 1" thick bottoms which give
enough weight down low that they self right from a "windows in the
water" knockdown. Here is a photo of the inside of Bob's IMB:

These boats can be operated totally from within the cabin, like an
automobile. No one need ever go on deck. For boating with children I
can see no equal.

These are cool boats. The tinted Plexiglass windows cut the sun's
power. The crew can always sit in the shade of the deck. Downdraft from
the sail cascades through the walkway slot.

IMB has an 8' long cabin on a wide multichine hull, sort of an enlarged
Piccup Pram hull.

I haven't really gotten a test report of this boat yet but the photo
above taken on its first sail shows to me that it must be pretty close
to "right". I did get a report from Bill Paxton who attended the
Houston meet and filed this report:

"All right, I admit it. When it comes to sailboats, I'm a size bigot.
Or at least I was until I took a ride in Bob Williams' IMB.

"I truly like the idea of Jim Michalak's "birdwatcher" designs. These
clever craft provide comfort and safety in boats that are easily
built by any novice. I've spent a lot of time studying JM's Jewelbox.
At 19' it's the largest of its type in Jim's repertoire. With a 12'
cabin, it could host a whole Cub Scout Pack. It's a little large for
my needs so I found myself pouring over Jim's Jewelbox Jr., a 16'
version with an 8' cabin. Nice. Scram Pram and even Eisbox were
considerations. But at no time did I seriously consider the IMB. Why?
It's too short! How can a cabin sailboat with a length of 13.5' be
taken seriously?

"Man, was I ever wrong!

"I met Bob Williams at the Lake Conroe Messabout, and I was
immediately fixated on his new IMB. He patiently answered all my
questions, and then, generous soul that he is, agreed to take me
along with him and Bob Shipman for a ride. (You'd be hard pressed to
find two finer sailing companions than the Bobs.)

"The first thing that impressed me was the volume of space in the
cabin. It' s 8' long. The three of us had plenty of space to sprawl
out, and at no time did I feel like we were getting in each other's
way. Skipper Bob mentioned that he had slept in the cabin Friday
night, and said it was downright spacious.

"A real surprise was the ease with which we could carry on a
conversation inside the cabin. The sound bounced around nicely making
it effortless to hear one another.

"The breeze was gusty and unreliable. At times we were really flying
along, and at other times we drifted from puff to puff. This gave me
a chance to see if the cabin would heat up. It got a degree or two
warmer than the 80 degree outside temperature, but that was about
all. When making any decent speed at all there was a fair amount of
breeze through the cabin.

"I enjoyed sitting in the shade as we sailed along. With the large
slot top down the middle it's impossible to stay in the shade all day
on all tacks, but it's way more solar protection than I get in the
open cockpit of my boat. I also like the idea of being able to stand
up and stretch while under sail.

"One of the things I was curious about was visibility. Would we
really be able to see well enough looking out the windows? The answer
is yes. I never felt we were in danger of other boats we failed to
see. But there's always the option to sit on the aft deck, steer with
your knees and swivel your head to your heart's content.

"Under the aft and fore decks are storage areas large enough to hold
camping supplies for one man for many days.

"Did I mention how easily the boat handled choppy water? Oh sure, the
wake from large powerboats tended to kill our speed when we hit them
head on. But the multi-chine hull gives the boat "soft shoulders,"
and it never felt like we were in any danger of being pushed over.

"Jim Michalak did a great job designing a boat that seems bigger on
the inside than on the outside. Bob Williams did a fine job of
building his IMB, Happy Camper, and I'm glad he brought it to Conroe.
It sure taught me a thing or two."

Prototype News

Some of you may know that in addition to the one buck catalog which
now contains 20 "done" boats, I offer another catalog of 20 unbuilt
prototypes. The buck catalog has on its last page a list and brief
description of the boats currently in the Catalog of Prototypes. That
catalog also contains some articles that I wrote for Messing About In
Boats and Boatbuilder magazines. The Catalog of Prototypes costs $3.
The both together amount to 50 pages for $4, an offer you may have
seen in Woodenboat ads. Payment must be in US funds. The banks here
won't accept anything else. (I've got a little stash of foreign
currency that I can admire but not spend.) I'm way too small for
credit cards.

Here are the prototypes abuilding that I know of:

Electron: The California Electron is coming along. Right now a four
cycle 2 hp outboard has been purchased so the original electric idea
may wait a while.

Mayfly: The prototype of the original 14' Mayfly is finished in New
York state. Here it is on its first sail (Long Island Sound).

The Queensland Campjon is about done. Waiting for a trailer.

A barn in rural Florida giving birth to the first Shanteuse, this one
stretched from 16' to 24'. The builder said it was easy to turn the
hull but it looks like his name is John Deere.